Inflatable mattress and control methods

ABSTRACT

A patient support, such as a mattress, includes a plurality of inflatable bladders. Depth sensors are included in the support that measure the degree of penetration of a patient into the mattress. An air pressure sensor is also included that measures the pressure inside at least one bladder. A suitable inflation level of the mattress is determined by monitoring the rate of change of the depth with respect to air pressure as the bladder is either inflated or deflated. By detecting an inflection point in the graphical relationship of the depth and pressure outputs, a suitable inflation point for the bladders is determined that reduced interface pressures experienced by the patient, yet does not overly sink the patient into the mattress to a degree or discomfort. Analyzing the outputs of the depth and pressure sensors can also be used to detect a patient&#39;s heart rate and respiration rate.

This application claims priority to U.S. provisional patent applicationSer. No. 61/696,819 filed Sep. 5, 2012 by applicants Patrick Lafleche etal. and entitled INFLATABLE MATTRESS AND CONTROL METHODS, the completedisclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to mattresses used for supportingindividuals thereon, and more particularly to mattresses that are usedin healthcare settings and that have one or more inflatable zones.

In health care settings, mattresses are used to support patientspositioned on beds, stretchers, cots, and the like. In many instances,such mattresses include one or more inflatable bladders whose inflationlevels can be controlled. In order to reduce the likelihood of thepatient developing bed sores, or aggravating pre-existing bed sores, theinflation level of the bladders should be set to so as to distribute thepatient's weight over as great an area as possible, or over an arealarge enough to reduce undesired force concentrations on the patient'sbody. By supporting the patient's weight over a greater surface area onthe mattress, the interface pressure between the patient and themattress is reduced. However, if the patient is allowed to sink toodeeply into the mattress, the patient may experience feelings ofdiscomfort. Further, it can be difficult for a caregiver to manuallydetermine a proper inflation level that sufficiently distributes thepatient's weight and that balances the patient's desire for comfort.

SUMMARY OF THE INVENTION

The various aspects of the present invention provide patient supports,such as mattresses, that have inflation levels that may be automaticallydetermined by one or more controllers, thereby avoiding the need forcaregivers to manually determine inflation levels. Further, the one ormore controllers determine inflation levels that are suitable for bothdistributing patient pressure, and thereby reducing bed sore sores, andfor creating a comfortable support surface for the patient. In someaspects, the mattress automatically determines a suitable inflationlevel for each individual patient that positions himself or herself onthe mattress, thereby creating an individualized inflation level that istailored to that specific individual. In other aspects, the mattressre-determines the suitable inflation level based on one or moretriggering events, such as, but not limited to, a patient re-enteringthe mattress, another individual positioning themselves on the mattress,an angular change of the entire mattress or of one section of themattress with respect to another, an object being positioned on themattress, or a person manually instructing the mattress to re-determinethe suitable inflation level. Still further, in some embodiments, thecontroller determines the suitable inflation level by monitoring therate of change of the patient immersion depth with respect to the rateof change of air pressure inside of the one or more bladders.

According to a first embodiment, a patient support is provided thatincludes an inflatable bladder, a depth sensor, an air pressure sensor,and a controller. The depth sensor generates a depth signal indicativeof how deeply a patient positioned on the patient support sinks into theinflatable bladder, and the air pressure sensor generates an airpressure signal indicative of a level of air pressure inside of theinflatable bladder. The controller determines a suitable inflation levelof the bladder by monitoring a rate of change of the depth signal withrespect to the air pressure signal as the air pressure inside thebladder is changed.

According to a second embodiment, a patient support is provided thatincludes an inflatable bladder, a first depth sensor, a second depthsensor, an air pressure sensor, and a controller. The first depth sensorgenerates a first depth signal indicative of how deeply a patientpositioned on the patient support sinks into a first portion of theinflatable bladder, and the second depth sensor generates a second depthsignal indicative of how deeply a patient positioned on said patientsupport sinks into a second portion of the inflatable bladder. The airpressure sensor generates an air pressure signal indicative of a levelof air pressure inside of the inflatable bladder. The controllerdetermines a suitable inflation level of the bladder by monitoring arate of change of the first depth signal with respect to the airpressure signal and by monitoring a rate of change of the second depthsignal with respect to the air pressure signal.

According to a third embodiment, a patient support is provided thatincludes a first section having a first inflatable bladder, a secondsection having a second inflatable bladder, a depth sensor, an airpressure sensor, and a controller. The second section is positioned inan area adapted to support a sacral region of a patient when the patientlies on the patient support. The depth sensor generates depth signalsindicative of how deeply a patient positioned on the patient supportsinks into the second inflatable bladder. The air pressure sensorgenerates air pressure signals indicative of a level of air pressureinside of the second inflatable bladder; and the controller determines asuitable inflation level of the second bladder based upon the depthsignals and the air pressure signals. The controller also determines asuitable inflation level of the first bladder based upon the suitableinflation level of the second bladder.

According to a fourth embodiment, a patient support is provided thatincludes an inflatable bladder, a depth sensor, an air pressure sensor,and a controller. The depth sensor generates a depth signal indicativeof how deeply a patient positioned on the patient support sinks into theinflatable bladder. The air pressure sensor generates an air pressuresignal indicative of a level of air pressure inside of the inflatablebladder. The controller determines a suitable inflation level of thebladder after a patient is positioned on the patient support. Thecontroller also automatically re-determines the suitable inflation levelafter at least one triggering event selected from the following: (1) thepatient exits the patient support and subsequently returns to thepatient support; (2) another person sits on the patient support; (3) anobject is placed on the patient support; (4) an angular orientation atleast a portion the patient support is changed; and (5) the patientmoves on the patient support more than a threshold amount.

According to a fifth embodiment, a method of controlling an inflationlevel of a plurality of inflatable bladders in a mattress is provided.The method includes measuring how far a patient sinks into a firstinflatable bladder; measuring how far a patient sinks into a secondinflatable bladder that is hermetically isolated from the firstinflatable bladder; and setting the air pressure inside both the firstand second inflatable bladders to a common inflation level that isdetermined based upon the depth measurement from at least one of thefirst and second inflatable bladders.

According to a sixth embodiment, a patient support is provided thatincludes a cover, first and second sections, a depth sensor, an airpressure sensor, an angle sensor, and a controller. The first sectionincludes a first inflatable bladder positioned inside of the cover in aregion of the mattress adapted to support a patient's back. The secondsection includes a second inflatable bladder positioned inside of thecover in a region of the mattress adapted to support a patient's sacralregion. The depth sensor generates depth signals indicative of howdeeply a patient positioned on said patient support sinks into thesecond inflatable bladder. The air pressure sensor generates airpressure signals indicative of a level of air pressure inside of thesecond inflatable bladder. The angle sensor generates angularmeasurement signals indicative of an angular orientation of the firstsection with respect to the second section, and the controllerdetermines a suitable inflation level of the second bladder based uponthe depth signals and the air pressure signals. The controller alsoautomatically re-determines the suitable inflation level if the angularsignals change by more than a threshold amount.

According to a seventh embodiment, a patient support is provided thatincludes an inflatable bladder, first and second depth sensors, and acontroller. The first depth sensor generates first depth signalsindicative of how deeply a patient positioned on the patient supportsinks into a first portion of the patient support. The second depthsensor generates second depth signals indicative of how deeply a patientpositioned on the patient support sinks into a second portion of thepatient support; and the controller monitors the first and second depthsignals to determine when a patient positioned on the patient supporthas moved more than a threshold amount. The controller alsoautomatically adjusts an inflation level inside of the inflatablebladder after the controller detects that the patient has moved morethan the threshold amount.

According to still other embodiments, any of the aforementioned sevenembodiments may be further modified to include any one or more of thefollowing features, steps, or characteristics, to the extent suchembodiments do not already include the following. The controller mayadapted determine the suitable inflation level after detecting aninflection point in a plot of the depth signals versus the air pressuresignals. The controller may monitors the rate of change of the depthsignals with respect to the air pressure signals as the air pressure islowered inside the bladder. Alternatively, the controller may monitorthe rate of change of the depth signals with respect to the air pressuresignals as the air pressure is raised inside the bladder.

The controller may set the suitable inflation level equal to an airpressure at which a derivative of the depth signal with respect to theair pressure signal is substantially equal to a local minimum. Theinflatable bladder may be incorporated into a mattress and positioned ata location adapted to support a patient's sacral area.

The inflatable bladder or bladders may all include pods.

The suitable inflation level may be determined without consulting anystored data previously gathered from multiple individuals of varyingweight and/or varying body morphology.

The depth sensor or depth sensors may be capacitive sensors. In someembodiments, the capacitive depth sensors include a capacitive platepositioned generally horizontally underneath the inflatable bladder, anda flexible, electrically conductive sheet positioned above theinflatable bladder.

The patient support may be incorporated into a bed frame having asupport surface thereon on which the patient support is supported. Thebed frame may include a control panel adapted to control inflation ofthe bladder. The control panel may further include a control for causingthe controller to re-determine the suitable inflation level whenmanipulated by a user.

The controller may re-determine the suitable inflation level byinflating the bladder to a desired pressure, allowing air to escape fromthe bladder, and monitoring the rate of change of the depth signals withrespect to the air pressure signals as the air pressure inside thebladder is decreased.

In some embodiment, one or more additional inflatable bladders may beincluded that do not include any depth sensors. Such additionalinflatable bladders may have their inflation levels set at one or morefixed ratios with respect to the suitable inflation level determined bythe controller. Alternatively, such additional inflatable bladders mayhave their inflation levels set at a fixed offset with respect to thesuitable inflation levels determined by the controller. Still further,in yet other embodiments, some of the additional bladders may have theirair pressure set at a fixed ratio with respect to the suitable inflationlevel, while others of the additional bladders may have their airpressure set at a fixed offset from the suitable inflation level.

The patient support may automatically re-determine the suitableinflation level when any one or more of the following triggering eventsoccur: movement of the patient on the patient support exceeds athreshold, angular changes are made to at least a portion of themattress, a patient moves onto the patient support, an additional personmoves onto the patient support, or an object is placed on the patientsupport.

One or more turning bladders may be included in the patient supportapparatus that are hermetically isolated from the other inflatablebladders and that are adapted to help turn a patient positioned on thepatient support when inflated. Such turn bladders may be positionedunderneath the inflatable bladder(s) having the depth sensor(s).

Third, fourth, and even more than four depth sensors may be used toprovide depth signals indicative of how deeply a patient positioned onthe patient support sinks into various portions of one or more bladders.The controller can monitor the multiple depth sensors to determinepatient movement and/or to determine a suitable inflation level for oneor more bladders in the patient support.

The suitable inflation level may be determined by controlling a releaseof air from, or an addition of air to, the inflatable bladder whilemonitoring the rates of change of the depth signals and the air pressuresignals.

According to yet another embodiment, a patient support is provided thatincludes an inflatable bladder, a depth sensor, an air pressure sensor,and a controller. The depth sensor generates a depth signal indicativeof how deeply a patient positioned on the patient support sinks into theinflatable bladder, and the air pressure sensor generates an airpressure signal indicative of a level of air pressure inside of theinflatable bladder. The controller monitors both changes in the depthand changes in the pressure and uses these changes to determine apatient's heart rate and/or respiration rate while positioned on thepatient support.

According to other aspects, the determination of heart and/orrespiration rate are performed non-invasively without having to connectany sensor to the patient. The monitoring of these vital signs isperformed automatically while the patient is positioned on the patientsupport. These vital signs are made available for transmission via awired or wireless connection to a remote location. These vital signs arealso made available for transmitting to the bed, stretcher, or cot onwhich the patient support is positioned.

Before the embodiments of the invention are explained in more detailbelow, it is to be understood that the invention is not limited to thedetails of operation or to the details of construction and thearrangement of the components set forth in the following description orillustrated in the drawings. The invention may be implemented in variousother embodiments and is capable of being practiced or being carried outin alternative ways not expressly disclosed herein. Also, it is to beunderstood that the phraseology and terminology used herein are for thepurpose of description and should not be regarded as limiting. The useof “including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. Further, enumeration may beused in the description of various embodiments. Unless otherwiseexpressly stated, the use of enumeration should not be construed aslimiting the invention to any specific order or number of components.Nor should the use of enumeration be construed as excluding from thescope of the invention any additional steps or components that might becombined with or into the enumerated steps or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation diagram of a patient support apparatus intowhich a patient support of the present invention may be integrated;

FIG. 2 is a plan view diagram of an embodiment of a patient supportaccording to the present invention;

FIG. 3 is a perspective view of the patient support of FIG. 2 shown witha cover removed;

FIG. 4 is a partial perspective view of a plurality of bladdersimplemented as pods that are included in the patient support of FIG. 2;

FIG. 5 is a perspective view of the patient support of FIG. 3 shown withthe bladders, foam, and other cushioning removed to illustrate thelayout of a plurality of depth sensors and a control box;

FIG. 6 is a partial, exploded view of the patient support of FIG. 2showing its internal components in the support's seat and back zones;

FIG. 7 is a schematic diagram of one embodiment of a control system thatmay be used in any of the patient supports described herein;

FIG. 8 is a flowchart illustrating an exemplary algorithm that may beused to determine a suitable inflation level for one or more bladderswithin any of the patient supports described herein;

FIG. 9 is a plot of exemplary data showing a relationship betweenimmersion depth and air bladder pressure when a patient is positioned onthe patient support and the air pressure is changed;

FIG. 10 is plot of different exemplary data showing a relationshipbetween immersion depth and air bladder pressure when a patient ispositioned on the patient support and the air pressure is changed; and

FIG. 11 is an illustrative screenshot that appears on a display and thatmay be used to control any of the patient supports described herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates a patient support 20 according to one embodiment ofthe invention. In the example of FIG. 1, patient support 20 is amattress. However, it will be understood that patient support 20 maytake on other manifestations, such as cushions, pads, etc. Indeed, inone embodiment, patient support 20 may be a cushion or pad for a chair,such as a wheelchair or a stationary chair. In general, patient support20 finds applicability wherever and whenever a patient is to besupported on a surface and it is desirable to reduce interface pressuresexperienced by the patient while positioned on the patient support.

In the embodiment shown in FIG. 1, patient support 20 is supported on apatient support apparatus 22 that, in this particular embodiment, is abed. Patient support apparatus 22 may take on other forms besides beds,such as, but not limited to, cots, stretchers, operating tables,gurneys, and the like. Patient support apparatus 22 may be aconventional support apparatus that is commercially available and thatmerely provides a supporting function for patient support 20. In otherembodiments, patient support apparatus 22 includes one or more controlsthat are integrated therein and which are used in controlling theoperation of patient support 20, as will be discussed in greater detailbelow.

As shown in FIG. 1, patient support apparatus 22 includes a base 24having a plurality of wheels 26, a pair of elevation adjustmentmechanisms 28 supported on base 24, a frame or litter 30 supported onelevation adjustment mechanisms 28, and a patient support deck 32supported on frame 30. Patient support apparatus 22 also includes aheadboard 34 and a footboard 36. Either or both of headboard 34 andfootboard 36 may be removable from frame 30 and may include one or moreelectrical connectors for establishing electrical communication betweenelectronic components on or in footboard 36 and/or headboard 34 andother electronic components supported on or in frame 30. Such electricalconnector(s) may include any one or more of the connectors disclosed incommonly assigned U.S. patent application Ser. No. 13/790,762, filedMar. 8, 2013, by applicants Krishna Bhimavarapu and entitled PATIENTSUPPORT APPARATUS CONNECTORS, the complete disclosure of which isincorporated herein by reference. Other types of connectors may also beused.

In one embodiment, electrical connectors are provided for establishingan electrical link between a user interface 38 that is positioned on, orintegrated into, footboard 36 and patient support 20. User interface maytake on a variety of different forms, such as, but not limited to, atouch screen, a Liquid Crystal Display (LCD), a plurality of buttons,switches, knobs, or the like, or any combination of these components. Aswill be described in more detail below, user interface 38 allows a userto control the operation of patient support 20. The electricalconnection between user interface 38 and patient support 20 may take ondifferent forms, including a direct electrical cable that runs fromfootboard 36 to patient support 20. In another embodiment, footboard 36include electrical connectors that electrically couple user interface 38to circuitry supported on frame 30. This circuitry is further inelectrical communication with a port (not shown) to which an electricalcable from patient support 20 may be inserted, thereby establishing anelectrical link between user interface 38 and patient support 20. Instill other embodiments, communication between user interface 38 andpatient support 20 is entirely wireless. An example of such wirelesscommunication is disclosed in commonly assigned, U.S. patent applicationSer. No. 13/802,992, filed Mar. 24, 2013, by applicants Michael Hayes etal. and entitled COMMUNICATION SYSTEMS FOR PATIENT SUPPORT APPARATUSES,the complete disclosure of which is hereby incorporated herein byreference.

Elevation adjustment mechanisms 28 are adapted to raise and lower frame30 with respect to base 24. Elevation adjustment mechanisms 28 may beimplemented as hydraulic actuators, electric actuators, or any othersuitable device for raising and lowering frame 30 with respect to base24. In the illustrated embodiment of FIG. 1, elevation adjustmentmechanisms 28 are operable independently so that the orientation offrame 30 with respect to base 24 may also be adjusted. This allowssupport apparatus 22 to tilt a patient supported on patient support 20to either the Trendelenburg orientation, or the reverse Trendelenburgorientation.

Frame 30 provides a structure for supporting patient support deck 32,headboard 34, and footboard 36. Patient support deck 32 provides asurface on which patient support 20 is positioned so that a patient maylie and/or sit thereon. Patient support deck 32 is made of a pluralityof sections, some of which may be pivotable about generally horizontalpivot axes. In the embodiment shown in FIG. 1, patient support deck 32includes a head or back section 40, a seat section 42, a thigh section44, and a foot section 46. In other embodiments, patient support deck 32may include fewer or greater numbers of sections. Head section 40, whichis also sometimes referred to as a Fowler section, is pivotable betweena generally horizontal orientation (shown in FIG. 1) and a plurality ofraised positions (not shown in FIG. 1). Thigh section 44 and footsection 46 may also be pivotable about horizontal pivot axes.

The general construction of any of base 24, elevation adjustmentmechanisms 28, frame 30, patient support deck 32, headboard 34, and/orfootboard 36 may take on any known or conventional design, such as, forexample, that disclosed in commonly assigned, U.S. Pat. No. 7,690,059issued to Lemire et al., and entitled HOSPITAL BED, the completedisclosure of which is incorporated herein by reference; or thatdisclosed in commonly assigned U.S. Pat. publication No. 2007/0163045filed by Becker et al. and entitled PATIENT HANDLING DEVICE INCLUDINGLOCAL STATUS INDICATION, ONE-TOUCH FOWLER ANGLE ADJUSTMENT, AND POWER-ONALARM CONFIGURATION, the complete disclosure of which is also herebyincorporated herein by reference. The construction of any of base 24,elevation adjustment mechanisms 28, frame 30, patient support deck 32,headboard 34, and/or footboard 36 may also take on forms different fromwhat is disclosed in the aforementioned patent and patent publication.

In some embodiments, the operation of patient support 20 is based atleast partially upon sensor data that originates from sensors integratedinto patient support apparatus 22, while in other embodiments, patientsupport 20 operates solely on sensor data originating from sensorspositioned internally inside of support 20. For those embodiments inwhich patient support 20 uses sensor data from patient support apparatus22, such sensor data includes angle data and/or weight data. Morespecifically, patient support apparatus 22, in some embodiments,includes one or more angle sensors that detect the angular orientation(with respect to horizontal) of frame 30, as well as one or more anglesensors that detect the angular orientation (with respect to horizontal)of one or more of the sections of support deck 32. Still further,patient support apparatus 22, in some embodiments, includes a load cellsystem that detects patient weight and/or a center of gravity of apatient positioned on patient support 20. One such load cell system thatmay be used in patient support apparatus 22 is disclosed in commonlyassigned U.S. Pat. No. 5,276,432 issued to Travis, the completedisclosure of which is incorporated herein by reference. Other load cellsystems may also be used. Regardless of the specific load cell systemused, patient support apparatus 22 may communicate any one or more ofpatient weight, patient center of gravity, the angular orientation offrame 30, and/or the angular orientation of one or more of deck sections40-46 to patient support 20, which may use this data in manners thatwill be discussed in more detail below.

As shown in FIG. 2, patient support 20 includes a head end 48, a footend 50, and a pair of sides 52. In the embodiment shown in FIG. 2, headend 48 of patient support 20 is intended to support a patients' headwhile foot end 50 is intended to support the patient's feet. Patientsupport 20 is further divided into a number of zones 54 that areillustrated in dashed lines in FIG. 2. Zones 54 represent areas ofpatient support 20 that can be controlled, in at least one aspect,differently from each other, and/or that are constructed differentlyfrom each other. For example, and as will be discussed in greater detailbelow, patient support 20 includes a right seat zone 58 a and a leftseat zone 58 b. Each seat zone 58 a and 58 b includes a correspondingbladder, and the inflation of the bladder in right seat zone 58 a can becontrolled independently of the inflation of the bladder in left seatzone 58 b.

As is also shown in FIG. 2, patient support 20 further includes a backzone 56, a thigh zone 60, and a foot zone 62. Back zone 56, in theillustrated embodiment, includes a head zone or pillow zone 64. Thephysical boundaries of each of the zones may be modified from thatshown, as well as the number of locations of each zone. In theembodiment of FIG. 2, back zone 56 is positioned such that it willgenerally be aligned with head or back section 40 of patient supportapparatus 22 when patient support 20 is positioned on support deck 32.Similarly, seat zone 58 will be generally aligned with seat section 42,thigh zone 60 will be generally aligned with thigh section 44, and footzone 62 will be generally aligned with foot section 46. Such alignment,however, is not necessary. Indeed, patient support 20 may be used onsupport apparatuses 22 in which the support deck 32 has no individualsections, or which has a fewer or greater number than the four shown inFIG. 1.

As was noted above, seat zone 58, in the embodiment shown in FIG. 2, issubdivided into right and left sides. That is, seat zone 58 includes aright seat zone 58 a and a left seat zone 58 b. Each of seat zones 58 aand 58 b define regions in which hermetically isolated bladders arepositioned so that the inflation level corresponding to right seat zone58 a can be controlled and/or set independently of the inflation levelcorresponding to left seat zone 58 b. In this manner, if a patient islying on his or her side, or is otherwise positioned closer to one side52 than the other, zones 58 a and 58 b can be set, at least in someembodiments, to different inflation levels. Alternatively, it may bedesirable to set the inflation levels for zones 58 a and 58 bdifferently in situations where the patient is positioned more towardthe middle of patient support 20. In alternative embodiments, seat zone58 could be a single zone that does not have separate subdivisionsbetween the right and left side, but rather was inflatable anddeflatable in a unitary manner. In still other alternative embodiments,one or more of the other zones 56, 60, and/or 62 could be subdividedinto left and right sub-zones, or sub-divided in still other manners.

FIG. 3 illustrates patient support 20 with its outer cover removed,exposing a plurality of inflatable pods 66, as well as a pillow bladder68, a foam crib 70 that supports pods 66, and a plurality of molded footend cushioning 72. Foam cushioning 72 is not inflatable, but insteadprovides cushioned support to a patient's feet through its softpliability. Inflatable pods 66 are fluidly coupled together in a mannerthat corresponds to zones 54. That is, all of the pods 66 within backzone 56 inflate and deflate together, and can be inflated and deflatedseparately from the pods 66 in any of the other zones. Similarly, all ofthe pods in right seat zone 58 a, all of the pods in left seat zone 58b, as well as all of the pods in thigh zone 60, are respectively able tobe inflated and deflated together, as well as separately from the pods66 in the other zones. Thus, the pods 66 in back zone 56 collectivelydefine a back bladder 74, the pods 66 in right seat zone 58 acollectively define a right seat bladder 76 a, the pods 66 in left seatzone 58 b collectively define a left seat bladder 76 b, and the pods 66in thigh zone 60 collectively define a thigh zone bladder 78. It will beunderstood that bladders 74, 76 a, 76 b, and/or 78 can be implemented,in alternative embodiments, in manners other than pods, such as, but notlimited to, elongated bladders, flat bladders, can-shaped bladders, orstill other shapes.

FIG. 4 provides greater detail of one embodiment of pods 66. Each pod 66includes a top surface 80, a base 82, and a sidewall 84. In at least oneof the pods 66 in each bladder or each zone 54, an opening 86 is definedthat is adapted to be coupled to an air hose 88. Air hose 88 extends toa pump box 90 (FIG. 5) which includes an air pump, blower, or othersource of air that may be supplied to air hose 88 for delivery to thecorresponding pods 66. As can be seen in FIG. 4, the pod 66 havingopening 86 defined in its base 82 further includes a plurality of sideopenings 92 defined in side wall 84 generally near base 82. Sideopenings 92 provide fluid communication with adjacent pods 66. Thus, airdelivered via hose 88 will be delivered not only to the pod 66 havingopening 86 defined in its base 82, but it will also be delivered to alladjacent pods that are in fluid communication with side openings 92.Those adjacent pods may further include their own side openings 92,which will further distribute the supplied air to more pods. Theinclusion of side openings 92 is arranged so that all of the pods 66within a given zone 54 or a defined bladder are interconnected by one ormore side openings 92. The pods at the edges of a zone 54 will notinclude side openings 92 in their exterior sides, thereby providingfluid isolation from neighboring zones. Consequently, all of the pods 66within a given zone 54 will be in fluid communication with each other,and will generally have the same air pressure. In some embodiments, morethan one air hose 88 may be connected to a given zone 54, and in someembodiments, separate air hoses 88 may be used for supplying air to thezone 54 and for removing air from the given zone 54. Regardless of theembodiment, control or pump box 90 oversees the delivery of air to,and/or the release of air from, the various zones 54.

FIG. 5 shows patient support 20 with all of the pods 66 and most of thefoam crib 70 removed therefrom. As can be seen, pump box 90 ispositioned at foot end 50 of patient support 20 and, while not shown,includes one or more pumps or blowers for supplying air to the pods 66,a manifold having an assembly of controllable valves for controlling theair pressure inside of each zone 54, as well as—in some embodiments—oneor more circuit boards for carrying out the control algorithms describedherein. As can also be seen in FIG. 5, patient support 20 furtherincludes a plurality of depth sensor plates 94 positioned generallylaterally across seat zone 58 of patient support 20. Depth sensor plates94 are used to measure how far a patient lying on the patient support 20has sunk into seat bladders 76 a and 76 b. Depth sensor plates 94 makethese measurements generally at the locations shown in FIG. 5. Thus, inthe embodiment of FIG. 5, where there are six total depth plates 94,three depth sensor plates 94 will make three measurements of patientdepth at three different, laterally spaced locations within right seatzone 58 a, while the three other depth sensor plates 94 will make threemeasurements of patient depth at three different, laterally spacedlocations within left seat zone 58 b. Collectively, depth sensor plates94 will make six depth measurements that span patient support 20 fromone side 52 to the opposite side 52 across seat zone 58.

As seen in FIG. 6, which illustrates various components of patientsupport 20 in back zone 56 and seat zone 58, patient support 20 includesa top cover 96, a fire barrier layer 100, a layer of conductive fabric98, pods 66, a fabric manifold 102, foam crib 70, a plurality of turningbladders 104, six depth sensor plates 94, and a bottom cover 106. Topcover 96 may be made of any conventional material used in themanufacture of hospital mattresses, such as, but not limited to, a knitpolyester, and/or a polyurethane.

Fire barrier 100 is positioned underneath top layer 96 and is made ofany suitable material that resists the spread of fire. Such materialsmay vary. In one embodiment, fire barrier 100 may be made of, orinclude, Kevlar® (poly-paraphenylene terephthalamide), or other brandsof para-aramid synthetic fibers. Other materials may alternatively beused.

Conductive fabric 98 functions to assist depth sensor plates 94 which,in the embodiment shown, are capacitive sensors whose output changes asa patient moves closer or farther away from them. More specifically,conductive fabric 98 functions in a manner similar to the top plate of aparallel plate capacitor, while depth sensor plates 94 form the bottomplates of the parallel plate capacitor. Thus, as the vertical distancebetween conductive fabric 98 and any of the depth sensor plates 94changes, the capacitance between the fabric 98 and the plate(s) 94 willchange. This change is detected by a detector circuit 112 (FIG. 7) thatis electrically coupled between fabric 98 and each of the depth sensorplates 94. That is, one or more wires (not shown) are electricallycoupled to fabric 98 and the detector circuits 112, while one or moreother wires (not shown) are connected between each plate 94 and thedetector circuit 112. Conductive fabric 98 may be any commerciallyavailable fabric that is electrically conductive, or it may be anelectrically conductive foil, or any other material that is electricallyconductive, and that is flexible enough to not significantly alter theflexibility of patient support 20 in that region.

Pods 66, as have been described herein, are inflated and deflated ingroups (zones 56, 58 a, 58 b, and 60) under the control of pump box 90and its associated control circuitry. The fluid connections between thepods 66 and pump box 90 are established by a plurality of hoses 88 thatrun between pump box 90 and various of the pods 66. Hoses 88 are housedwithin fabric manifold 102. Hoses 88 each include one or more connectors108 for fluidly connecting the hose to one or more of the pods 66.

Turn bladders 104 are positioned underneath foam crib 70 and are used tohelp turn a patient positioned on top of patient support 20. To thatend, turn bladders 104 extend generally longitudinally in a directionfrom head end 48 to foot end 50 and are each separately andindependently inflatable and deflatable. The inflation of turn bladders104 is controlled by pump box 90 and its associated circuitry.

Each sensor plate 94 is a generally planar sheet of electricallyconductive material, such as copper or other electrically conductivematerial. Each sensor plate 94 is electrically isolated from the othersensor plates 94. An insulation and shielding layer 110 is positionedunderneath the sensor plates 94. Insulation and shielding layer 110, inone embodiment, includes upper and lower electrically insulating layersthat surround six electrical shields. The electrical shields areelectrically conductive and may be electrically coupled to thecapacitive detector circuits 112 (FIG. 7). The electrical shields serveto limit capacitive interference that might otherwise result from themetal components of frame 30 of patient support apparatus 22.

FIG. 7 shows one embodiment of a control system 114 that may beimplemented to control patient support 20 in the manners describedherein. Other types, arrangements, and/or configurations of controlsystems may alternatively be used. Control system 114 includes acontroller 116, a user interface 118, and a plurality of depth sensors120. User interface 118 may be the same as user interface 38, discussedabove, which is incorporated into footboard 36 of patient supportapparatus 22, or it may be stand-alone user interface. Such stand-aloneuser interfaces may include user interfaces that are incorporated intopedestals that may be removable mounted on patient beds, such as patientsupport apparatus 22. In the embodiment shown in FIG. 7, user interface118 is a touch screen. It will be understood that other types of userinterfaces may be used, including buttons, switches, knobs, lights,and/or displays.

Each depth sensor 120 includes one of depth sensors plates 94, acorresponding detector 112, conductive fabric 98, and, in someembodiments, a shield (not shown) positioned underneath the sensor plate94. Detector 112 may be any circuitry capable of detecting the varyingcapacitance between plate 94 and conductive fabric 98. In oneembodiment, detector 112 includes an AD7747 capacitance-to-digitalconverter manufactured by Analog Devices of Norwood, Mass. Other typesof detector circuitry may be used in other embodiments. Whatever thecircuitry used, detectors 112 detect the capacitance levels betweenplates 94 and conductive fabric 98, which provide an indication of thevertical distance between plates 94 and fabric 98, which in turnindicates how deeply a patient is currently immersed in different areasof seat zone 58. In the embodiment illustrated, there are six separatedetector circuits 112, thereby generating six separate measurements ofpatient depth in the seat zone 58. In one embodiment, depth sensors 120each generate capacitive measurements multiple times a second, while inother embodiments, measurements are made at different frequencies.

Controller 116 is in electrical communication with both user interface118 and depth sensors 120, as well as a plurality of air pressuresensors 122 and, in the illustrated embodiment, one or more tilt sensors124. Air pressure sensors 122 measure the current air pressure insideeach of the bladders of patient support 20 (e.g. back bladder 74, seatbladders 76 a and 76 b, thigh bladder 78, and pillow bladder 68). As wasnoted, each of these bladders generally corresponds to zones 56, 58 a,58 b, 60, and 64, respectively. Tilt sensors 124 measure the angularorientation one or more portions of patient support 20, and/or theymeasure the entire angular orientation of patient support 20. In someembodiments, as was discussed previously, tilt sensors 124 are omittedand patient support 20 instead receives tilt data from one or more anglesensors that are incorporated into patient support apparatus 22. Instill other embodiments, patient support 20 is implemented without anytilt sensors 124, and without receiving any tilt data from patientsupport apparatus 22.

Controller 116, in the embodiment shown in FIG. 7, includes two separatecircuit boards: a sensor circuit board 126 and a main control circuitboard 128. Sensor circuit board 126 receives the electrical signals fromall of the various sensors and oversees the operation of these sensors(e.g. depth sensors 120, air pressure sensors 122, and tilt sensors124). The data gathered from these various sensors is forwarded fromsensor circuit board 126 to main control circuit board 128. In theembodiment shown, this data is forwarded via a serial peripheralinterface (SPI) bus, although it will be understood that other buses maybe used for this purpose. Main circuit board 128 is programmed, orotherwise configured, to carry out the control algorithms that will bedescribed in more detail below. Generally speaking, main circuit board128 determines the suitable inflation levels (e.g. a desired airpressure or—for those bladders with depth sensors 120—a desired patientdepth) for all of the various bladders and controls necessary valves,air pump, and other aspects necessary to implement and maintain thosesuitable inflation levels. More specifically, main circuit board 128 isin communication with an air pump control 130 and a plurality ofdeflation valves 132. By way of suitable electrical signals sent to pumpcontrol 130 and valves 132, main control board 128 is able to implementand maintain the suitable inflation levels of the various bladders.

At shown in FIG. 7, each board 126 and 128 includes a processor, whichmay be a microprocessor or a microcontroller. Indeed, each circuit board126 and 128 may include any electrical component, or group of electricalcomponents, that are capable of carrying out the algorithms describedherein. In many embodiments, circuit boards 126 and 128 will bemicroprocessor based, although not all such embodiments need include amicroprocessor. In general, circuit boards 126 and 128 will include anyone or more microprocessors, microcontrollers, field programmable gatearrays, systems on a chip, volatile or nonvolatile memory, discretecircuitry, and/or other hardware, software, or firmware that is capableof carrying out the functions described herein, as would be known to oneof ordinary skill in the art. Such components can be physicallyconfigured in any suitable manner, such as by mounting them to one ormore circuit boards, or arranging them in other manners, whethercombined into a single unit or distributed across multiple units. Itwill further understood by those skilled in the art that controller 116may be implemented in different forms from the two boards 126 and 128illustrated in FIG. 7. Such variations may include combining thefunctions of both boards 126 and 128 onto a single board, or furtherdistributing the functions of these boards onto more than the two boards126 and 128 shown in FIG. 7.

FIG. 8 illustrates an inflation control algorithm 134 that, in oneembodiment, is carried out by controller 116. Controller 116 may carryout this algorithm in different manners. In one manner, algorithm 134 issplit amongst boards 126 and 128, while in another manner, all of thesteps of algorithm 134 are carried out by main control board 128.Regardless of the specific manner of implementing control algorithm 134,inflation control algorithm 134 begins at an initial step 136 in whichcontroller 116 waits for a user command to start the algorithm. The usercommand originates from user interface 118 after a user, such as a nurseor other caregiver, presses a button, touches a touch screen, orotherwise manipulates a control thereon that indicates he or she wishesto have patient support 20 automatically determine a suitable inflationlevel for the bladders of patient support 20. Initial step 136 maycommence with a patient either on or off of patient support 20. If itcommences with no patient supported on patient support 20, a patientmust be positioned on patient support 20 prior to the commencement ofstep 140, discussed below.

After controller 116 receives a start command at initial step 136, itproceeds to an inflation step 138 where it begins inflating all of thebladders to a preset upper threshold. This is carried out by sendingappropriate control signals to air pump control 130 and closing and/oropening the necessary valves so that air is delivered from pump box 90to the bladders. While other variations may be made, controller 116inflates all of the bladders of patient support 20 at step 138 with thesole exception of the turning bladders 104. More specifically,controller 116 inflates back bladder 74, seat bladders 76 a, and 76 b,and thigh zone bladder 78 to the preset upper threshold. In theembodiment shown in FIG. 8, the preset upper threshold is an airpressure equal to 35 millimeters of mercury (mmHg), although differentthresholds can be used. In general, the upper threshold is set so thatthe patient sinks in very little, if at all, at the upper thresholdinflation level. Controller 116 carries out this inflation in a closedloop manner, receiving feedback from pressure sensors 122. Each zone 54includes at least one pressure sensor that repetitively indicates tocontroller 116 the current air pressure inside of that zone. Controller116 is therefore able to monitor the pressure inside each of the zones54 as they are being inflated toward the threshold pressure, andterminates the inflation for each zone 54 once it reaches the upperthreshold pressure.

After the completion of step 138, controller 116 moves onto deflationstep 140. As was noted above, deflation step 140 should not commenceuntil a patient is positioned on patient support 20. In someembodiments, controller 116 is programmed to not even start inflationstep 138 until a patient is positioned on the patient support.Controller 116 may determine patient presence and absence on patientsupport via communication with the load cells built into patient supportapparatus 22 that can detect patient weight, or patient support 20 maydetermine patient presence by including its own sensors. In otherembodiments, controller 116 starts control algorithm 134 regardless ofwhether a patient is present on patient support 20, and it is up to thecaregiver to ensure a patient is positioned thereon prior to initiatingthe start command at step 136.

During deflation step 140, controller 116 begins deflating the airinside of right and left seat zones 58 a and 58 b. While deflating theright and left bladders 76 a and 76 b in these zones 58 a and 58 b,respectively, controller 116 continuously records measurements of depthfrom each of the six depth sensors 120 while also continuously recordingmeasurements of air pressure inside of right and left seat bladders 76and 76 b. These measurements are recorded in a memory (not shown)accessible to controller 116, or on a memory within controller 116.These measurements are recorded in a manner that preserves therelationship between depth and pressure as the bladders is deflated. Inother words, a measurement of depth and pressure are both madesimultaneously, or nearly simultaneously, at a given time, andcontroller 116 records in memory that these two values correspond intime with each other. This enables controller 116 to know what the depthreading was for a given pressure, or vice versa.

FIGS. 9 and 10 show two examples that graphically plot the data whichcontroller 116 is recording during step 140. While controller 116 doesnot actually plot this data, the plots of FIGS. 9 and 10 provide auseful way of illustrating the type of data that controller 116 isgenerating, and the subsequent analyses of this data that it performs.In both of these FIGS., the air pressure measurements are shown plottedon the x-axis, while the depth measurements from one of the depthsensors 120 are shown on the y-axis. Further, in both of these diagrams,the x-axis shows the air pressure in reverse order, that is, the airpressure decreases from left to right. This is done merely as onepossible example. The x and y axes could be reversed, and the order ofthe pressure values could be change, if desired. For each depth sensor120, controller 116 stores the depth sensor data that was gathered forthat depth sensor 120 along with the corresponding air pressure datathat was recorded simultaneously, or nearly simultaneously, with thedepth sensors measurements. FIGS. 9 and 10 show a depth-versus-pressureplot 144 of this data. The data used to generate these plots 144 ismerely exemplary of the types of data that may be gathered by controller116 for a particular patient after controller 116 proceeds through steps136-140 of algorithm 134.

Upon completing deflation step 140, controller 116 proceeds to aderivative calculation step 142. During derivative calculation step 142,controller 116 computes the mathematical derivative of the depthmeasurements with respect to the air pressure measurements for theentire set of depth and pressure measurements obtained during step 140.That is, controller 116 computes the rate of change of depth withrespect to air pressure for each of the six depth sensors 120. For thethree right-most depth sensors 120, the air pressure data will be thesame because the three right-most depth sensors 120 are all positionedunderneath right seat bladder 76 a, which is a single bladder having asingle air pressure. Similarly, for the three left-most depth sensors120, the air pressure data will be the same for each other (but notnecessarily the same as for the right-most depth sensors) because allthree of these left-most sensors 120 are positioned underneath left seatbladder 76 b, which is also a single bladder having a single airpressure. The depth measurements made by depth sensors 120, in contrast,may, and likely will, be different for each depth sensor because thepatient's varying weight and morphology across the different portions ofzones 58 a and 58 b or bladders 76 a and 76 b.

FIGS. 9 and 10 show graphically a derivative calculation plot 146 thatcorresponds to the depth-versus-pressure plots 144 in each of theseFIGS. In other words, plot 146 in FIG. 9 is a plot of the derivative ofcurve 144 in FIG. 9, while plot 146 in FIG. 10 is a plot of thederivative of curve 144 in FIG. 10. The plots 144 and 146 need notactually be graphically displayed by control system 114, but controller116 calculates the underlying data of each of these plots. Thedifference between the graphs in FIGS. 9 and 10 is presented here tomerely show different examples of the types of data that control system114 will generate during the performance of algorithm 134. In an actualsystem, data corresponding to six different graphs will be generated bycontroller 116—one for each of the six depth sensors 120. This data isthen analyzed in accordance with algorithm 134 to determine a suitableinflation level (defined in terms of air pressure, patient depth, orsome other control variable) for the various bladders of patient support20.

After computing the derivatives of the depth-versus-pressure data foreach of the depth sensors 120 at step 142, controller 116 moves to step148 where it analyzes the calculated derivatives to see if any of thesix sets of depth-versus-pressure data (one for each of the six depthsensors 120) have any derivative values that meet a threshold criteria.In the specific algorithm 134 shown in FIG. 8., the threshold is set atany derivatives which have a value less than five burst counts (BC) permillimeter of mercury (mmHG). The term “burst counts” refers to theoutputs of the capacitive detector circuits 112 which, in the embodimentshown, measure capacitance using a charge count method. It will, ofcourse, be understood by those skilled in the art that other methods ofmeasuring capacitance may be used, including, but not limited to,oscillator-based approaches, bridge approaches, and still otherapproaches. It will further be understood by those skilled in the artthat other methods of measuring patient depth may be used besidecapacitive sensors, such at, but not limited to, inductive sensors,infrared light sensors, or other sensors. Regardless of the type ofsensor, controller 116 analyzes the slope of the depth-versus-pressuredata and looks for any slopes that exceed a threshold maximum value, orare less than a threshold minimum value, and that value may be definedin whatever terms are appropriate for that particular sensor. In theillustrated example, the slope is shown defined in terms of burst countsper millimeter of mercury. Other units may be used.

If controller 116 does not detect any slopes that meet the criteriadefined in derivative analysis step 148, then controller 116 returns tostep 140 where it continues deflating the bladders, gathering more data,and repeating steps 140, 142, and 144. This loop will continue until atleast one derivative is found that matches the criteria of step 148. (Itshould be noted that the threshold criteria of step 148 is set so that,unless a patient is mistakenly absent from patient support 20 duringalgorithm 134, the criteria of step 148 will be fulfilled for at leastone depth sensor 120 at some point during the deflation of patientsupport 20.) Once controller 116 determines that the derivative of thedepth-versus-pressure data from at least one depth sensor 120 has atleast one value that meets the threshold of step 148, controller 116moves to selection step 150.

At selection step 150, controller 116 determines whether there is morethan one depth sensor 120 that has a derivate plot 146 that, at somepoint in the plot, exceeds the threshold defined in step 148. If so,controller 116 selects which data from the multiple depth sensors 120meeting the criteria of step 148 to use. In other words, selection step150 involves selecting which of the six depth sensors 120 has generateddata that controller 116 is going to use in determining the suitableinflation level of seat bladder 76. Controller 116 makes this selectionby choosing which derivative plot 146 has the largest negative value.This means that controller 116 looks at the data from the sensors 120and chooses the sensor 120 where the depth-versus-pressure plot 144 hasthe steepest downward slope.

An example of this choice can be seen graphically by examining FIGS. 9and 10. Suppose, for purposes of illustration, that FIG. 9 graphicallydepicted the data generated by a first one of depth sensors 120, andthat FIG. 10 graphically depicted the data generated by a second one ofdepth sensors 120. Further, suppose that both of the derivative plots ofFIGS. 9 and 10 met the criteria of step 148 of algorithm 134 and thatcontroller 116 was confronted with having to choose which set of data touse—that of FIG. 9 or that of FIG. 10. A visual comparison of FIGS. 9and 10 reveals that the depth-versus-pressure plot 144 of FIG. 9 has asteeper downward slope than the plot 144 of FIG. 10. Accordingly,controller 116 will choose to use the data from the depth sensors 120that corresponds to FIG. 9.

After selecting the depth sensor 120 to use at selection step 150,controller 116 moves to step 152, where it determines whether thederivative of the depth-versus-pressure plot 144 for the depth sensor120 selected at step 150 has reached a local minimum 154 (FIGS. 9 and10). If no local minimum in the derivative plot 146 has yet beenreached, controller 116 returns to step 140 and repeats the stepspreviously described. At some point, after repeating any necessarysteps, controller 116 will eventually determine at step 152 that a localminimum in the derivative curve 146 has been reached for one of thedepth sensors 120. When that determination is made, controller 116 movesto a re-inflation step 156.

At re-inflation step 156, controller 116 starts inflating the bladders76 a and 76 b of seat zones 58 a and 58 b until the air pressure insideof them reaches the air pressure corresponding to the air pressure atthe local minimum 154 identified in step 152. In other words, whencontroller 116 eventually determines the first local minimum at step152, controller 116 has successfully determined the desired inflationlevel of seat zone 58—it is either the air pressure corresponding tothat local minimum, or it is the depth corresponding to that localminimum, which are alternative ways of achieving the same thing. Inother words, controller 116 at step 156 will re-inflate the seatbladders until either the air pressure reaches the air pressurecorresponding to local minimum 154, or until the currently measureddepth reaches the depth corresponding to local minimum 154. The resultshould be the same in either case.

FIGS. 9 and/or 10 can be used to illustrate this more clearly. Suppose,for example, that the data of FIG. 9 was the data used by controller 116in determining whether a local minimum 154 had been reached at step 152.While FIG. 9 shows multiple local minimums 154, this is for illustrationpurposes only. Because algorithm 134 generates data during the deflationof patient support 20 (as opposed to during the inflation of patientsupport 20), the left-most local minimum 154 shown in FIG. 9 will be thefirst (and likely only) local minimum detected by controller 116. Theadditional local minima 154 to the right of this might be detected,depending upon how close they are to the first local minimum, and/ordepending upon how much additional data controller 116 is configured togather. However, regardless of whether or not multiple local minima 154are detected, controller 116 selects the first local minimum 154 andsets the suitable inflation level, graphically indicated by line 158 inFIG. 9, equal to either the air pressure measurement or depthmeasurement that correspond to it. In other words, suitable inflationlevel 158 in FIG. 9 identifies both an air pressure and a depth. The airpressure it defines is approximately 13 mmHG in this example. The depthit identifies is approximately 1.5 inches of immersion into patientsupport 20 (the depth at the intersection of plot 144 and line 158). Atstep 156, controller 116 re-inflates seat bladders 76 a and 76 b untileither the air pressure inside of them equals 13 mmHg, or the depthsensor that generated the data of FIG. 9 detects a depth ofapproximately 1.5 inches. This is the suitable level of inflation forseat zones 58 a and 58 b.

At steps 160 and 162, controller 116 determines the suitable levels ofinflation for back bladder 74 and thigh bladder 78, which correspond toback zone 56 and thigh zone 60, respectively. In the embodiment shown inFIG. 8, algorithm 134 sets both of these inflation levels equal to anair pressure that is a fixed offset from the air pressure inside of seatzone 58. More specifically, at step 160, controller 116 sets the airpressure inside of back bladder 74 to a value that is X mmHg less thanthe air pressure inside of seat bladders 76 a and 76 b. The specificvalue of X may vary. In one embodiment, X is set equal to 10 mmHg. Inother embodiments, X may take on other values. Thus, continuing with theexample of FIG. 9, if controller 116 has determined the local minimum154 is at 13 mmHg, and therefore has set the air pressure inside of seatbladders 76 equal to 13 mmHg, controller 116 will set the pressureinside of back bladder 74 at step 160 equal to 13 minus X mmHg, or inthis specific example, 3 mmHg (13−10=3).

After setting the air pressure inside of back bladder 74 at step 160,controller 116 proceeds to step 162 where it adjusts the air pressureinside of the thigh bladder 78. In the embodiment of algorithm 134 shownin FIG. 9, controller 116 sets the thigh zone air pressure to be a valuethat is Y mmHg greater than the air pressure inside of seat bladders 76a and 76 b. As with the value of X, the value of Y may also vary. In oneembodiment, Y is equal to 5 mmHg. In other embodiments, other values maybe used. Continuing with the example of FIG. 9, controller 116 would setthe air pressure inside of thigh bladder 78 equal to 18 mmHg, which isfive mmHg (Y) greater than the air pressure inside of seat bladders 76 aand 76 b (13 mmHg).

In an alternative embodiment, algorithm 134 is modified so that one orboth of steps 160 and 162 used fixed ratios, rather than offsets fromthe air pressure inside of seat bladders 76 a and 76 b. In other words,for example, controller 116 will set the air pressure inside of backbladder 74 equal to an air pressure that matches a preset ratio withrespect to the air pressure inside of seat bladders 76 a and 76 b. Forexample, step 160 could be modified so that controller 116 sets the backbladder pressure to be equal to, say, 90% of the seat zone air pressure.Similarly, step 162 could be modified so that controller 116 set thethigh zone air pressure to be equal to 105%, or some other fixed ratiovalue, of the air pressure inside of seat bladders 76 a and 76 b. Stillfurther, in some embodiments, algorithm 134 is modified so that one ofthe thigh and back bladders is set as an offset from the seat zone airpressure, while the other of the thigh and back bladders has their airpressure set as a percentage of the seat zone air pressure.

It will further be understood that patient support 20 can be modified toinclude one or more depth sensors 120 in either or both of back zone 56and thigh zone 60, in which case steps 160 and/or 162 of algorithm 134would be modified so that the air pressure inside of the bladderscorresponding to these zones was set in the same manner as the airpressure inside of seat zone 58 was set in steps 136 through 156 ofalgorithm 134. Still further, patient support 20 could be modified toinclude one or more bladders in foot zone 62, and the air pressureinside of those bladders could be set by using one or more depth sensorspositioned therein, or by setting the air pressure as an offset to, orratio of, the air pressure inside of another bladder.

After controller 116 completes step 162, it has completed algorithm 134.Algorithm 134 will then terminate and controller 116 will maintain thepressures inside of the seat, back, and thigh zone bladders at thosedetermined in steps 156, 160, and 162, respectively. Pressure inside ofhead or pillow bladder 68 may be set the same as that in back bladder74, or it may be set differently.

In the embodiment shown, algorithm 134 is triggered based upon a userstart command. In an alternative embodiment, step 136 of algorithm 134is modified so that algorithm 134 will commence upon the occurrence ofone or more triggering events. In one embodiment, the triggering eventsthat will cause algorithm 134 to start include all of the following: auser initiates a start command via user interface 118; control system114 determines that a patient has entered patient support 20 or patientsupport apparatus 22; control system 114 determines that a patient haschanged positions on patient support 20 (e.g. turning, sitting up,rolling to one side or the other, etc.); control system 114 determinesthat an angular orientation of one of deck sections 40, 42, 44, or 46has changed; control system 114 determines that the orientation of frameor litter 30 has changed (such as by adjusting elevation adjustmentmechanisms 28 different amounts); and control system 114 detects thatanother object or another patient has entered or exited patient support20. In yet other alternative embodiments, step 136 of algorithm 134 canbe modified so that algorithm 134 will commence upon any subset of thesetriggering events, or any combination of one or more of these triggeringevents and any one or more other triggering events not specificallyidentified in the foregoing list.

When algorithm 134 is modified to include additional triggering eventsbeyond a user manually initiating a start command, control system 114can be configured to detect these additional triggering events inmultiple different manners. Thus, for example, control system 114 candetermine that a patient has entered patient support 20 bycommunications it receives from a control system onboard patient supportapparatus 22 that includes load cells positioned to detect a patient'sweight (and also, by implication, the absence or presence of a patient).The information from the load cells can also be used to detect whenanother patient or object enters or exits patient support 20 due to asignificant weight change detected by the load cells. Similarly, patientmovement on patient support 20 can be detected by the load cells ofpatient support apparatus 22 because such movement will result inchanges in the patient's center of gravity, which can be detected by theload cells in the manner disclosed in the aforementioned and commonlyassigned U.S. Pat. No. 5,276,432 issued to Travis. Angular changes dueto the movement of any of deck sections 40, 42, 44, and 46 can becommunicated to control system 114 from a controller on board patientsupport apparatus 22 that is in communication with angle sensors thatmeasure the angles of these various deck sections. Similar angle sensorson patient support apparatus 22 can be used to detect, and report tocontrol system 114, the angular orientation of frame 30. Alternatively,one or more angular sensors can be incorporated into patient support 20so that changes in can be detected directly by control system 114,rather than relying on communication from components external to patientsupport 20.

Regardless of the specific number and kind of triggering events thatcause controller 116 to re-start algorithm 134, theautomatically-triggered operation of algorithm 134 helps ensure that apatient is supported on patient support 20 at suitable inflation levels,regardless of changes that are made which affect those inflation levels,and regardless of whether or not a caregiver is present. Thus, patientsupport 20 is, in at least one embodiment, configured to automatically,and repetitively, determine a suitable inflation level for theparticular patient positioned thereon, and to update that inflationlevel appropriately based upon changes that affect the suitability ofthe inflation level. Further, because the suitable or desired inflationlevel is automatically chosen in a manner that reduces interfacepressure (as will be discussed more below), patient support 20 willautomatically adjust its inflation levels so that the likelihood of apatient developing pressure sores is reduced, regardless of caregiverpresence, and regardless of changes that might otherwise lead toincreases in interface pressure. In other words, patient support 20 willautomatically adjust its inflation level based on triggering events sothat the inflation level will be set at a level that generallyminimizes, or comes close to minimizing, the interface pressure thepatient is experiencing, thereby reducing the likelihood of pressuresores developing. Further, this will be done without requiring that aweight measurement of the patient first be taken, or any estimates ofthe patient size, morphology, or other patient aspects be made by acaregiver.

In yet another alternative embodiment, algorithm 134 can be modified sothat, instead of gathering data while deflating seat bladders 76 a and76 b, data was gathered while inflating these seat bladders. That is,algorithm 134 would start out by deflating—if not already deflated—theseat zone bladders until a preset minimum pressure was set. Thereafter,controller 116 would begin inflating the seat zone bladders while takingrepetitive measurements of air pressure and depth for each of the sixdepth sensors 120. This would result in generating the data of FIGS. 9and 10, for example, in a manner from right to left, rather than theleft to right manner of the unmodified algorithm 134. It is expectedthat the result of this data gathering would be the same. Controller 116would then choose the local minimum 154 that was detected last, insteadof first, as the point defining the desired inflation level. Algorithm134 would stop gathering data once a threshold maximum air pressure wasreached, such as the 35 mmHg defined in step 138.

In yet another embodiment of algorithm 134, the suitable or desiredlevel of inflation inside of seat bladders 76 a and 76 b is setindependently. That is, instead of using data from one of the six depthsensors 120 to use for determining the inflation level of both bladders76 a and 76 b, algorithm 134 can be modified so that data from one ofthe three depth sensors 120 under right seat bladder 76 a is selectedfor determining the suitable inflation level of right seat bladder 76 a,while data from one of the other three depth sensors 120 under left seatbladder 76 b is selected for determining the suitable inflation level ofleft seat bladder 76 b. The air pressure inside of the back and thighzones can then be set to be either an offset to, or percentage of, aselected one of seat bladders 76 a and 76 b. Still further, patientsupport 20 can be modified to include a greater or smaller number ofseat zone bladders 76, in which case algorithm 134 can becorrespondingly modified.

It will further be understood by those skilled in the art that patientsupport 20 can be modified to include a greater, or lesser, number ofdepth sensors 120 than the six shown in the accompanying drawings. Inone embodiment, only a single depth sensor is used, in which casealgorithm 134 is modified to omit selection step 150, which is no longernecessary. Still further, the placement of the depth sensors 120 can bemodified, such as, but not limited to, positioning one or more of thedepth sensors 120 underneath one or more of the other bladders inpatient support 20.

FIG. 11 illustrates one example of an image 164 that may be displayed ona touch screen, or other display screen, of user interface 118. Image164 includes an “optimal” icon 166, a “firmer” icon 168, and a “softer”icon 170. Pressing on icon 166 will trigger controller 116 to runthrough algorithm 134, which will result in setting the inflation levelsinside of patient support 20 at a level that is designed to minimize, ornearly minimize, the patient interface pressures experienced by thepatient. If it is desired to alter those automatically determinedinflation levels, a caregiver can press either of icons 168 or 170.Pressing icon 168 will cause controller 116 to increase the air pressureinside of all of the bladders 74, 76 a, 76 b, and, 78 an incrementalamount. Pressing it N times will cause controller 116 to increase theair pressure N times the incremental amount, up to a safety limit,beyond which further inflation will not take place. Conversely, pressingicon 170 will cause controller 116 to decrease the air pressure insideof all of the bladders 74, 76 a, 76 b, and 78 an incremental amount, andpressing it N time will cause controller 116 to decrease the airpressure N times the incremental amount.

Image 164 of FIG. 11 also includes a patient positioning icon 172, apulmonary icon 174, a pressure redistribution icon 176, and amicroclimate icon 178. Image 164 will change depending upon which ofthese four icons a user presses (or otherwise selects). The image 164shown in FIG. 11 is the image that corresponds to pressure distributionicon 176 being selected. If a user selects patient position icon 172, adifferent image will appear on the touch screen that include icons forcontrolling turning bladders 104. Pressing those icons will causecontroller 116 to control the inflation and deflation of turningbladders 104 in the desired manner. If a user selects pulmonary icon174, a different image will appear on the touch screen that includesicons for controlling pulmonary therapies that patient support 20 iscapable of carrying out, such as percussion, or other therapies.Pressing one of these icons will thereby cause controller 116 toinstitute the inflation and deflation of the appropriate bladdersnecessary to carry out these therapies. Finally, if a user selectsmicroclimate icon 178, this will cause yet a different image to appearon the touch screen that includes icons for controlling the microclimateaspects of patient support 20. Specifically, in one embodiment, patientsupport 20 is a low air loss mattress in which air can be made tocontinuously flow upward from patient support 20 to cool and/or dry themicroclimate at the interface of the patient and patient support 20.

In addition to illustrating a graphical representation of the pressureand depth data that is generated by algorithm 134, FIGS. 9 and 10 alsoshow patient interface pressure, which is not measured by patientsupport 20, but has been included on FIGS. 9 and 10 for purposes ofdemonstrating the usefulness of algorithm 134. Specifically, each ofFIGS. 9 and 10 include a patient interface pressure plot 180 that showsthe interface pressure that a patient experiences at the correspondingair pressures. The scale for the units of the patient interface pressureis not shown in FIGS. 9 and 10, but the absolute value of the interfacepressure is not as important as illustrating that the desired inflationlevel 158 is at, or very near, the minimum in the patient interfacepressure 180. This is true for the plots shown in both FIGS. 9 and 10.Thus, it can be seen that algorithm 134 automatically determines aninflation level that minimizes, or nearly minimizes, the patientinterface pressure, which is important for reducing the likelihood ofbed sores.

In addition to the modifications already discussed above, algorithm 134may be further modified in still additional manners. In one embodiment,instead of searching for the first local minimum (left-most in FIGS. 9and 10) in the derivative curve 146, controller 116 could be programmedto search for, and identify, the second local minimum 154. This secondlocal minimum could then be used to define the suitable inflation level158. Alternatively, controller 116 could be programmed to pick an airpressure that was somewhere between the first and second local minima154. Still further, algorithm 134 could be modified to select an airpressure or depth that was a fixed offset from either the first orsecond local minima 154.

Stepping back from the details of algorithm 134, it can be observed thatalgorithm 134 monitors how much a patient sinks in relation to how muchair is let out of the underlying seat bladders 76 a and 76 b. That is,after inflating bladders to the pressure of step 138, for eachincremental release of air from bladders 76 a, 76 b, controller 116monitors how much farther the patient sinks into bladders 76 a, 76 b. Atfirst, the release of air causes very little change in pressure. This isseen in FIGS. 9 and 10, which show a generally straight and onlyslightly negatively sloped line 144 in the region from 50 mmHg down toroughly 20 to 25 mmHg. At about this region of the curve, furtherdecreases in the air pressure (caused by releasing more air frombladders 76 a, 76 b) lead to a more precipitous increase in theimmersion depth of the patient. It is believed that this is due to thefact that, in the region of the more steeply sloped section of curves144, decrease in air volume (and air pressure) result predominantly in aperson sinking into the mattress more, with little additional newsurface area added between the top of patient support 20 and the patienthimself. In other words, in the generally flat region of curves 144(e.g. approximately 25 to 50 mmHg), it is believed that the predominantreaction of the system (patient and patient support 20) to furtherdecreases in air pressure is to bring more and more of the surface areaof the patient's body into contact with the top of patient support 20,while in the in the more steeply sloped section of curves 144, the morepredominant reaction of the system is for the patient to sink infurther, without much accompanying increase in the surface area of thepatient's body that comes into contact with the top of patient support20. Because increasing the surface area of the patient's body that comesinto contact with patient support 20 is generally desired—because thegreater surface area better distributes the patient's weight, thusdecreasing patient interface pressure—further decreases in the airpressure in the generally flat regions of curves 144 lead morepredominantly to distributing the patient's weight (as opposed tosinking into the surface). In contrast, in the more curved region ofcurves 144, further decrease in air pressure lead to greater changes indepth, as opposed to greater changes in surface area. Thus, decreasingthe air pressure much past the beginning of the generally curved regionsof curves 144 does little more to alleviate patient interface pressure.Consequently, selecting an air pressure in the region of curves 144where the steeper slope starts leads to an air pressure that minimizes,or nearly minimizes, the patient interface pressure, which is whysuitable inflation lines 158 are positioned in this region.

Controller 116 is thereby able to determine a optimized, or nearlyoptimized, level of inflation for seat bladders 76 a, 76 b, that reducespatient interface pressures to nearly as small as possible, while alsopreventing, to the extent possible, the over-immersion of a patient inpatient support 20, which can lead to feelings of discomfort to thepatient. Controller 116 is able to do this without resort to any look-uptables that store desired pressure values, or desired depths, forvarious types of patients, based on their weight, height, morphology, orother characteristics. Instead, controller 116 is able to uniquelytailor the inflation level of the bladders in patient support so as toprovide an optimized level of interface pressure reduction and patientcomfort to each individual that rests on patient support 20. Further, aswas noted, this optimized level of inflation is, in at least oneembodiment, automatically adjusted any time a triggering event occursthat may lead to the currently set level of inflation no longer beingthe optimized level. Some of such triggering events were discussedpreviously.

It will be understood that, while algorithm 134 was described above interms of gathering air pressure and depth data, it could be modified togather air bladder volume and depth data. That is, instead of makingmeasurements of air pressure as air is allowed to escape during step140, measurements could instead be made of the volume of air that isreleased from the bladder, and/or the volume of air remaining in thebladder. This volume data would be gathered in conjunction with thedepth measurements. Controller 116 would then look for an inflectionpoint in the graph of this data, just as it does in the graph of the airpressure versus depth data described above.

In another embodiment, controller 116 is configured to non-invasivelymonitor a patient's vital signs while the patient is positioned onpatient support 20. This non-invasive monitoring of the patient's vitalsigns is carried out, in some embodiments, completely independently ofthe algorithms used to set the inflation level of the bladders. That is,regardless of how the inflation levels of the bladders are chosen and/orcontrolled, controller 116 is configured in some embodiments todetermine either or both of a patient's heart rate and respiration rate.

When so configured, controller 116 determines a patient's heart rateand/or respiration rate by monitoring the outputs from both the pressuresensors 122 and the depth sensors 120. More specifically, in oneembodiment, pressure and depth readings are monitored and compared toeach other. When graphically represented, with the pressure readings onone axis and the depth readings on another axis, the data collected fromthese sensors will vary generally sinusoidally in response to thepatient's breathing and respiration. These sinusoidal signals can beprocessed to determine both the patient's breathing rate and heart rate.Such processing can be accomplished by a variety of different means,such as, but not limited to, performing Fourier transforms on the dataand identifying peak frequencies corresponding to those within theexpected range of heart rates and the expected range of respirationrates.

A more detailed description of suitable processing of the depth andpressure measurements to determine heart rate and respiration rate isfound in commonly assigned U.S. Pat. No. 7,699,784 issued Apr. 20, 2010to applicants Wan Fong et al. and entitled SYSTEM FOR DETECTING ANDMONITORING VITAL SIGNS, the complete disclosure of which is herebyincorporated herein by reference. Although this '784 patent describes asystem for determining a patient's heart rate and breathing rate byanalyzing signals generated from force sensors positioned under thepatient, the same analysis can be applied to the pressure and depthsignals generated from sensors 122 and 120 to yield heart rate andbreathing rate.

The above description is that of several embodiments of the invention.Various alterations and changes can be made from these embodimentswithout departing from the spirit and broader aspects of the inventionas defined in the appended claims, which are to be interpreted inaccordance with the principles of patent law including the doctrine ofequivalents. This disclosure is presented for illustrative purposes andshould not be interpreted as an exhaustive description of allembodiments of the invention or to limit the scope of the claims to thespecific elements illustrated or described in connection with theseembodiments. For example, and without limitation, any individualelement(s) of the described invention may be replaced by alternativeelements that provide substantially similar functionality or otherwiseprovide adequate operation. This includes, for example, presently knownalternative elements, such as those that might be currently known to oneskilled in the art, and alternative elements that may be developed inthe future, such as those that one skilled in the art might, upondevelopment, recognize as an alternative. Further, the disclosedembodiments include a plurality of features that are described inconcert and that might cooperatively provide a collection of benefits.The present invention is not limited to only those embodiments thatinclude all of these features or that provide all of the statedbenefits, except to the extent otherwise expressly set forth in theissued claims. Any reference to claim elements in the singular, forexample, using the articles “a,” “an,” “the” or “said,” is not to beconstrued as limiting the element to the singular.

What is claimed is:
 1. A patient support comprising: an inflatablebladder; a depth sensor adapted to generate a depth signal indicative ofhow deeply a patient positioned on said patient support sinks into saidinflatable bladder; an air pressure sensor adapted to generate an airpressure signal indicative of a level of air pressure inside of saidinflatable bladder; and a controller adapted to determine a suitableinflation level of said bladder by monitoring a rate of change of thedepth signal with respect to the air pressure signal as the air pressureinside the bladder is changed.
 2. The support of claim 1 wherein saidcontroller determines the suitable inflation level after detecting aninflection point in a plot of the depth signal versus the air pressuresignal.
 3. The support of claim 1 wherein the controller monitors therate of change of the depth signal with respect to the air pressuresignal as the air pressure is lowered inside the bladder.
 4. The supportof claim 1 wherein the controller monitors the rate of change of thedepth signal with respect to the air pressure signal as the air pressureis raised inside the bladder.
 5. The support of claim 1 wherein saidcontroller sets the suitable inflation level equal to an air pressure atwhich a derivative of the depth signal with respect to the air pressuresignal is substantially equal to a local minimum.
 6. The support ofclaim 1 wherein said inflatable bladder is incorporated into a mattressand positioned at a location adapted to support a patient's sacral area.7. The support of claim 1 wherein said patient support includes: aplurality of inflatable bladders; a plurality of depth sensors, eachdepth sensor positioned inside a corresponding one of said plurality ofinflatable bladders, and each depth sensor adapted to generate a depthsignal indicative of how deeply a patient positioned on the patientsupport sinks into the corresponding inflatable bladder; a plurality ofair pressure sensors, each air pressure sensor adapted to generate anair pressure signal indicative of a level of air pressure inside of acorresponding one of said inflatable bladders; and wherein saidcontroller is adapted to determine the suitable inflation level based onall of the depth signals and all of the air pressure signals.
 8. Thesupport of claim 1 wherein said patient support further includes a bedframe having a support surface on which said bladder may be supported,said bed frame including a control panel adapted to control inflation ofsaid bladder, said control panel including a control for causing saidcontroller to re-determine said suitable inflation level.
 9. The supportof claim 1 wherein said bladder is incorporated into a mattresspositionable on a bed frame, and said controller automaticallyre-determines the suitable inflation level if more than a thresholdamount of patient movement is detected, or if an angular orientation ofa portion of the bed frame changes by more than a threshold angularamount.
 10. The support of claim 1 wherein said depth sensor includes acapacitive plate positioned generally horizontally underneath saidbladder, and a flexible, electrically conductive sheet positioned abovesaid bladder.
 11. A patient support comprising: a first inflatablebladder; a second inflatable bladder; a depth sensor adapted to generatea depth signal indicative of how deeply a patient positioned on saidpatient support sinks into said first inflatable bladder; an airpressure sensor adapted to generate an air pressure signal indicative ofa level of air pressure inside of said first inflatable bladder; and acontroller adapted to determine a suitable inflation level of said firstinflatable bladder based upon readings from said depth sensor, saidcontroller further adapted to control an air pressure inside of saidsecond bladder so as to be equal to a fixed ratio with respect to, or tohave a fixed offset from, the air pressure inside of said firstinflatable bladder.
 12. A patient support comprising: an inflatablebladder; a first depth sensor adapted to generate a first depth signalindicative of how deeply a patient positioned on said patient supportsinks into a first portion of said inflatable bladder; a second depthsensor adapted to generate a second depth signal indicative of howdeeply a patient positioned on said patient support sinks into a secondportion of said inflatable bladder; an air pressure sensor adapted togenerate an air pressure signal indicative of a level of air pressureinside of said inflatable bladder; and a controller adapted to determinea suitable inflation level of said bladder by monitoring a rate ofchange of the first depth signal with respect to the air pressure signaland by monitoring a rate of change of the second depth signal withrespect to the air pressure signal.
 13. The support of claim 12 whereinsaid controller sets the suitable inflation level equal to an airpressure at which a derivative of either the first depth signal withrespect to the air pressure signal or the second depth signal withrespect to the air pressure signal is substantially equal to a localminimum.
 14. The support of claim 12 wherein said inflatable bladder isincorporated into a mattress and positioned at a location adapted tosupport a patient's sacral area, and said inflatable bladder includes aplurality of pods.
 15. The support of claim 12 wherein said first depthsensor includes: (1) a first capacitive plate positioned generallyhorizontally underneath said first portion of said bladder, and (2) aflexible, electrically conductive sheet positioned above said bladder;and said second depth sensor includes: (1) a second capacitive platepositioned generally horizontally underneath said second portion of saidbladder, and (2) said flexible, electrically conductive sheet.
 16. Thesupport of claim 12 wherein said controller re-determines the suitableinflation level by inflating the bladder to a desired pressure, allowingair to escape from said bladder, and monitoring the rate of change ofthe first and second depth signals with respect to the air pressuresignal as the air pressure inside the bladder is decreased.
 17. Apatient support comprising: a first section having a first inflatablebladder, a second section having a second inflatable bladder, saidsecond section being positioned in an area adapted to support a sacralregion of a patient when the patient lies on the patient support; adepth sensor adapted to generate depth signals indicative of how deeplya patient positioned on said patient support sinks into said secondinflatable bladder; an air pressure sensor adapted to generate airpressure signals indicative of a level of air pressure inside of saidsecond inflatable bladder; and a controller adapted to determine asuitable inflation level of said second bladder based upon said depthsignals and said air pressure signals, and to determine a suitableinflation level of said first bladder based upon the suitable inflationlevel of said second bladder.
 18. The support of claim 17 wherein saidsuitable inflation level of said first bladder is a fixed ratio, or hasa fixed offset, with respect to the suitable inflation level of saidsecond bladder.
 19. The support of claim 17 wherein said controllerdetermines the suitable inflation level of said second bladder bymonitoring a rate of change of the depth signals with respect to the airpressure signals as the air pressure inside the bladder is changed. 20.The support of claim 17 wherein said first and second bladders bothinclude a plurality of pods.
 21. The support of claim 17 furtherincluding a third section having a third inflatable bladder, said thirdsection being positioned on a side of said second section opposite saidfirst section; and wherein said controller is adapted to determine asuitable inflation level of said third bladder based upon the suitableinflation level of said second bladder.
 22. The support of claim 21wherein said suitable inflation level of said third bladder has anotherfixed ratio, or fixed offset, with respect to the suitable inflationlevel of said second bladder.
 23. The support of claim 21 furtherincluding a plurality of depth sensors for generating a plurality ofdepth signals indicative of how deeply a patient positioned on saidpatient support sinks into a plurality of different portions of saidsecond inflatable bladder, wherein said controller determines thesuitable inflation level of said second bladder by monitoring all ofsaid plurality of depth signals.
 24. The support of claim 23 whereinsaid controller determines the suitable inflation level of said secondbladder by monitoring the rate of change of the depth signals withrespect to the air pressure signals for each of the plurality of depthsensors.
 25. The support of claim 24 wherein said controller determinesthe suitable inflation level of said second bladder by determining whichof said plurality of depth sensors has the highest rate of change of itsdepth signal with respect to the air pressure signal.